SPOJ GSS3 Can you answer these queries III

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
using namespace std;

#define maxn  50010
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1

struct SegNode{
int lsum,rsum,sum,ans;
};

SegNode tree[maxn<<2];

void PushUp(int rt){
tree[rt].sum = tree[rt<<1].sum + tree[rt<<1|1].sum;
tree[rt].lsum = max(tree[rt<<1].lsum , tree[rt<<1].sum + tree[rt<<1|1].lsum);
tree[rt].rsum = max(tree[rt<<1|1].rsum , tree[rt<<1|1].sum + tree[rt<<1].rsum);
tree[rt].ans = max(max(tree[rt<<1].ans , tree[rt<<1|1].ans),tree[rt<<1].rsum + tree[rt<<1|1].lsum);
}

void build(int l,int r,int rt){
if(l == r){
scanf("%d",&tree[rt].sum);
tree[rt].lsum = tree[rt].rsum = tree[rt].ans = tree[rt].sum;
return ;
}
int m = (l + r)/2;
build(lson);
build(rson);
PushUp(rt);
}

void update(int pos,int val,int l,int r,int rt){
if(l == r){
tree[rt].lsum = tree[rt].rsum = tree[rt].ans = tree[rt].sum = val;
return ;
}
int m = (l + r)/2;
if(pos <= m) update(pos , val , lson);
else update(pos , val , rson);
PushUp(rt);
}

SegNode query(int L,int R,int l,int r,int rt){
if(L <= l && r <= R){
return tree[rt];
}
int m = (l + r)/2;
if(R <= m) return query(L , R , lson);
else if(L > m) return query(L , R , rson);
else{
SegNode result,left,right;
left = query(L , m ,lson);
right = query(m + 1, R, rson);
result.sum = left.sum + right.sum;
result.lsum = max(left.lsum , left.sum + right.lsum);
result.rsum = max(right.rsum , right.sum + left.rsum);
result.ans = max(max(left.ans , right.ans), left.rsum + right.lsum);
return result;
}
}

int n,m,op,a,b;
int main()
{
while(~scanf("%d",&n)){
build(1 , n , 1);
scanf("%d",&m);
while(m --){
scanf("%d %d %d",&op,&a,&b);
if(op == 1)
printf("%d\n",query(a , b, 1 , n , 1).ans);
else
update(a, b, 1, n, 1);
}
}
return 0;
}